Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3217
2016-02-09T14:04:47ZAsymmetric light transmission by using 2D PT-symmetric photonic nanostructure
http://hdl.handle.net/2117/76340
Asymmetric light transmission by using 2D PT-symmetric photonic nanostructure
Turduev, M.; Botey Cumella, Muriel; Herrero Simon, Ramon; Kurt, H.; Staliunas, Kestutis; Giden, I.
We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.
2015-07-27T11:42:50ZTurduev, M.Botey Cumella, MurielHerrero Simon, RamonKurt, H.Staliunas, KestutisGiden, I.We propose for the first time a simple realization of a two-dimensional Parity-Time symmetric hexagonal shaped photonic structure composed of honeycomb lattice. The structure has a symmetric periodic modulation of the refractive index on the wavelength scale, which is combined with an anti-symmetric gain/loss distribution on the same scale. That leads to non-reciprocal light coupling at resonant frequencies. The design of the realistic structure is based on a simple physical concept: alternating low index cylinders with gain and loss in a honeycomb configuration, embedded in a higher index dielectric background.Suppression of modulation instability by spatio-temporal modulation
http://hdl.handle.net/2117/28105
Suppression of modulation instability by spatio-temporal modulation
Staliunas, Kestutis
Modulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.
2015-05-29T15:05:10ZStaliunas, KestutisModulation Instability (MI) is at the basis of spontaneous pattern formation in many nonlinear spatially extended systems in Nature, technologies, and in everyday live. In spite of variety of spatial patterns in different systems, the very onset of a spatio-temporal dynamics, the breaking of initial spatial and temporal symmetry, is initiated by MI. The said is valid for dissipative nonlinear systems, where dissipative patterns set in, but also for conservative systems. The examples in latter case ranges from the filamentation of light in Kerr-nonlinear media, instabilities of Bose condensates with attractive interactions, to perhaps, the recently much discussed formation of the “rogue waves”.Beam focusing in chirped mirror with a defect
http://hdl.handle.net/2117/27767
Beam focusing in chirped mirror with a defect
Cheng, Yu Chieh; Staliunas, Kestutis
Recently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.
2015-05-06T09:53:50ZCheng, Yu ChiehStaliunas, KestutisRecently the beam focusing in reflection from chirped dielectric mirror has been proposed and demonstrated, where the negative (anomalous) diffraction is responsible for this flat mirror focusing. For a strong focusing performance (large focal distance), a wide angular range of strong (negative) angular dispersion is required. We show that a defect layer in the dielectric mirror (one layer is of a double size), can increase the angular dispersion, and thus improve the focusing performance. By introducing a defect layer in the chirped mirror, the focal distances can be increase from 12 µm up to 22 µm in a specific, calculated, structure, as our numerical integration show.Excitation/inhibition patterns in a system of coupled cortical columns
http://hdl.handle.net/2117/27684
Excitation/inhibition patterns in a system of coupled cortical columns
Malagarriga Guasch, Daniel; Villa, Alessandro; García Ojalvo, Jordi; Pons Rivero, Antonio Javier
We study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and all-to-all coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.
2015-04-30T08:53:32ZMalagarriga Guasch, DanielVilla, AlessandroGarcía Ojalvo, JordiPons Rivero, Antonio JavierWe study how excitation and inhibition are distributed mesoscopically in small brain regions, by means of a computational model of coupled cortical columns described by neural mass models. Two cortical columns coupled bidirectionally through both excitatory and inhibitory connections can spontaneously organize in a regime in which one of the columns is purely excitatory and the other is purely inhibitory, provided the excitatory and inhibitory coupling strengths are adequately tuned. We also study the case of three columns in different coupling configurations (linear array and all-to-all coupling), finding abrupt transitions between heterogeneous and homogeneous excitatory/inhibitory patterns and strong multistability in their distribution.Beam focalization by chirped mirrors
http://hdl.handle.net/2117/27289
Beam focalization by chirped mirrors
Cheng, Yu Chieh; Peckus, Martynas; Kicas, Simonas; Trull Silvestre, José Francisco; Cojocaru, Crina; Vilaseca Alavedra, Ramon; Drazdys, Ramutis; Staliunas, Kestutis
A novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.
2015-04-13T14:59:48ZCheng, Yu ChiehPeckus, MartynasKicas, SimonasTrull Silvestre, José FranciscoCojocaru, CrinaVilaseca Alavedra, RamonDrazdys, RamutisStaliunas, KestutisA novel application of chirped dielectric mirrors for narrow beam focalization is proposed and demonstrated numerically and experimentally. Analogy to temporal dispersion compensation by chirped dielectric mirrors is discussed.Asymmetric transmission from a 2D PT-symmetric honeycomb nanostructure
http://hdl.handle.net/2117/24628
Asymmetric transmission from a 2D PT-symmetric honeycomb nanostructure
Botey Cumella, Muriel; Herrero Simon, Ramon; Turduev, M.; Zhao, D.; Giden, I.; Kurt, H.; Staliunas, Kestutis
We propose a simple realization of a 2-dimensonal (2D) PT-symmetric photonic structure: a honeycomb arrangement of alternating cylinders with gain or loss in a dielectric background. The structure provides a periodic modulation of the refractive index on the wave length scale, which combined with an anti-symmetric gain/loss distribution on the same scale, leads to non-reciprocal light coupling at resonance frequencies. Numerical simulations show asymmetric right-left transmission of light beams.
2014-11-10T10:26:15ZBotey Cumella, MurielHerrero Simon, RamonTurduev, M.Zhao, D.Giden, I.Kurt, H.Staliunas, KestutisWe propose a simple realization of a 2-dimensonal (2D) PT-symmetric photonic structure: a honeycomb arrangement of alternating cylinders with gain or loss in a dielectric background. The structure provides a periodic modulation of the refractive index on the wave length scale, which combined with an anti-symmetric gain/loss distribution on the same scale, leads to non-reciprocal light coupling at resonance frequencies. Numerical simulations show asymmetric right-left transmission of light beams.Managing spatial diffraction through a periodic loss modulation
http://hdl.handle.net/2117/24442
Managing spatial diffraction through a periodic loss modulation
Botey Cumella, Muriel; Pradeep Kumar, Nikhil; Herrero Simon, Ramon; Maigyte, Lina; Staliunas, Kestutis
We show that periodic distributions of gain or losses on the wavelength scale allow managing spatial diffraction of light beams, with no index contrast. It has been recently predicted that such artificial periodic structures, analogous to Photonic Crystals (PhCs), would also hold the novel spatial beam propagation effects reported for PhCs such as subdiffraction propagation, self-collimation, spatial filtering or beam focusing by a lens with flat interfaces. In particular, we consider an ideal periodic 2-dimensional (2D) arrangement of lossy cylinders embedded in air. We analytically show that this loss distribution affects diffraction. Indeed, a significant focusing behind a thin flat-flat crystal slab is observed, following the estimation of anomalous spatial dispersion for specific frequency ranges. Besides, close to the edges of the first Brillouin Zone, the light intensity map of a Gaussian beam exiting the lossy structure exhibits a high transmission windows instead of the transmission stop band expected for PhCs. This results from the strong anisotropic attenuation provided by the loss periodicity. Finally, we also consider a more realistic system with combined modulations of refractive index and losses: a 2D metallic photonic crystal (MPhC). We demonstrate that MPhCs also support selfcollimation and focusing, being such effects associated to zero and negative diffraction respectively. Finally, due to the anisotropic attenuation of light, the structure is also able to spatially filter noisy beams.
2014-10-22T08:56:34ZBotey Cumella, MurielPradeep Kumar, NikhilHerrero Simon, RamonMaigyte, LinaStaliunas, KestutisWe show that periodic distributions of gain or losses on the wavelength scale allow managing spatial diffraction of light beams, with no index contrast. It has been recently predicted that such artificial periodic structures, analogous to Photonic Crystals (PhCs), would also hold the novel spatial beam propagation effects reported for PhCs such as subdiffraction propagation, self-collimation, spatial filtering or beam focusing by a lens with flat interfaces. In particular, we consider an ideal periodic 2-dimensional (2D) arrangement of lossy cylinders embedded in air. We analytically show that this loss distribution affects diffraction. Indeed, a significant focusing behind a thin flat-flat crystal slab is observed, following the estimation of anomalous spatial dispersion for specific frequency ranges. Besides, close to the edges of the first Brillouin Zone, the light intensity map of a Gaussian beam exiting the lossy structure exhibits a high transmission windows instead of the transmission stop band expected for PhCs. This results from the strong anisotropic attenuation provided by the loss periodicity. Finally, we also consider a more realistic system with combined modulations of refractive index and losses: a 2D metallic photonic crystal (MPhC). We demonstrate that MPhCs also support selfcollimation and focusing, being such effects associated to zero and negative diffraction respectively. Finally, due to the anisotropic attenuation of light, the structure is also able to spatially filter noisy beams.Climate networks at inter-annual and intra-season time scales constructed via ordinal time-series analysis
http://hdl.handle.net/2117/22697
Climate networks at inter-annual and intra-season time scales constructed via ordinal time-series analysis
Deza, Juan Ignacio; Barreiro, Marcelo; Masoller Alonso, Cristina
2014-04-25T10:46:57ZDeza, Juan IgnacioBarreiro, MarceloMasoller Alonso, CristinaControl and enhancement of beam quality of broadarea semiconductor devices and arrays by multimode interference couplers and two-dimensional gain modulation
http://hdl.handle.net/2117/21961
Control and enhancement of beam quality of broadarea semiconductor devices and arrays by multimode interference couplers and two-dimensional gain modulation
Murad, M.; Sorel, M.; Herrero Simon, Ramon; Botey Cumella, Muriel; Marsh, J.H.; Staliunas, Kestutis
It is proposed to control the beam quality of broad-area semiconductor devices by two-dimensional structuring enforcing phase coherence across the device. First results based on MMI couplers are presented.
2014-03-10T12:09:24ZMurad, M.Sorel, M.Herrero Simon, RamonBotey Cumella, MurielMarsh, J.H.Staliunas, KestutisIt is proposed to control the beam quality of broad-area semiconductor devices by two-dimensional structuring enforcing phase coherence across the device. First results based on MMI couplers are presented.Negative diffraction by a periodically modulated loss
http://hdl.handle.net/2117/21078
Negative diffraction by a periodically modulated loss
Botey Cumella, Muriel; Pradeep Kumar, Nikhil; Herrero Simon, Ramon; Maigyte, Lina; Picó, Ruben; Staliunas, Kestutis
2013-12-20T12:37:37ZBotey Cumella, MurielPradeep Kumar, NikhilHerrero Simon, RamonMaigyte, LinaPicó, RubenStaliunas, Kestutis